The present invention relates to a heating system for conveyor pipes which transport through them fluid such as a heavy oil or the like.
In general, a heavy oil or other similar fluid which has solidifiability, or viscosity increasing property under a low temperature, and undergoes thermal decomposition or other chemical phenomenon at a high temperature deteriorates in fluidity thereof in the winter season in which an atmospheric temperature is lower, because it is increased in the viscosity thereof. Therefore, in order to allow such a fluid to be smoothly conveyed through a conveyor pipe under a lower atmospheric temperature, provisions are made to heat the pipe, thereby decreasing the viscosity of the fluid which tends to increase. In a conventional heating system for conveyor pipes, the steam-trace heating method is executed by using a trap. The steam-trace heating method is available as two types. One of these two types is that a heating pipe is installed, and it is only formed with a steam layer therein to use the latent heat of the steam for heating the conveyor pipe, and the other is that a condensation layer is allowed to stay within the separately installed heating pipe, thereby utilizing the sensible heat thereof as well as the latent heat of the steam which is allowed to exit in the form of a layer.
However, in the former type heating method in which a steam layer is only formed within the heating pipe to use the latent heat of the steam, overheating is locally introduced on the contact surfaces of the heating pipe and the conveyor pipe with each other, or the heat to the conveyor pipe is excessively great in quantity, whereby it is difficult that the heating temperature to the conveyor pipe is held to a suitable range.
Also, the latter type heating method in which a condensation layer is allowed to stay in the heating pipe, the condensation layer is subjected to a temperature gradient on the downstream side thereof, and therefore, it is substantially impossible to know a total of precise quantity of heat given to the conveyor pipe. For this reason, it is difficult to estimate temperatures of the conveyor pipe and fluid flowing therethrough such as a heavy oil, which are to be heated. This is a disadvantage of the heating method in which a condensation layer is allowed to stay in the heating pipe.
Therefore, a counterproposal is made such as an electric heater system long in size which heats the conveyor pipe evenly at any longitudinal portion thereof. However, this electric heating system threatens excessive heating of the conveyor pipe, while at the same time, the electric heating system undergoes a problem in which it can not be applied to any conveyor pipe conveying therethrough a heavy oil or any other similar fluid which requires explosion-proof provisions to be made.
It is therefore an object of the present invention to provide for an explosion-proof heating system for conveyor pipes transporting therethrough a heavy oil or other similar fluid, in which they are longitudinally heated evenly at any portion of them to a predetermined temperature, and which is feasible of installing works thereof.